How old was ABBA when she made Dancing Queen?

ABBA is a Swedish pop group that consists of four members: Agnetha Fältskog, Björn Ulvaeus, Benny Andersson, and Anni-Frid Lyngstad. The band was formed in 1972 and released their hit song "Dancing Queen" in 1976. Since ABBA is a group, it doesn't make sense to talk about their age when "Dancing Queen" was released.